Signal seeking receiver



Dec. 20, 1949 v. H. WILEY SIGNAL SEEKING RECEIVER Filed sept. 16, 1944 Patented Dec. 20, 1949 UNITED STATES PATENT OFFICE SIGNAL SEEKING RECEIVER Verls H. Wiley, Kenmore, N. Y., assignor to Colonial Radio Corporation, Buffalo, N. Y.

Application September 1.6, 1944, Serial No. 554,470

(Cl. Z50-20) 9 Claims. 1

This invention relates to improvements in automatic tuning apparatus of the type in Which a tuning instrumentality such as a variable condenser or inductance is operated by a motor and the tuning variation is stopped automatically as soon as the circuit or circuits desired to be tuned have reached resonance.

Circuits of this nature are shown and described in the co-pending application of William S. Winiield, Serial No. 463,775, filed October 29, 1942, in which the fundamental principles of such apparatus are discussed. The invention herein is applicable to signal-seeking receivers, one form of which is described in my earlier application, Serial' No. 534,389, led May 6, 1944.

In signal-seeking receivers, also sometimes called stop-on-carrier receivers or signaltuned receivers, the tuning instrumentality is driven by a motor and scans the entire spectrum within the range of the receiver. When an incoming signal is tuned in, the voltage produced by the signal operates a control tube, which in turn, operates a relay opening the motor circuit so that the receiver remains tuned to the incoming signal. Receivers of this type are particularly advantageous for use in automobiles because the receiver may be operated as a pushbutton receiver without the necessity of resetting the pushbuttons whenever the vehicle travels to a different area.

It is necessary that such a receiver shall stop only on an incoming signal of predetermined strength; i. e., one which is strong enough to give good reception, but the receiver must be free from false stoppage caused by noise or static impulses. In accordance with my invention I have been able to produce a receiver which is for all practical purposes entirely immune to such false stoppages.

With such a receiver installed in an automobile, I have been able to follow trolley cars Where the noise level was so high that it completely masked any but the very strongest local signals, and under such circumstances have been able to operate the receiver throughout the entire spectrum, the receiver selecting and stopping on not only local signals but also on weak distant signals without any false stoppage due to noise or static.

From the foregoing it will be understood that it is an object of this invention to provide a signal-seeking receiver which will unfailingly stop at an incoming signal even under extreme conditions of noise and static, and which is free from false stoppages resulting from noise or static.

It is still a further object of this invention to provide such a receiver in which this result is obtained without the sacrice of sensitivity.

Still other objects and advantages of my invention will be apparent from the specification.

The features of novelty which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its fundamental principles and as to its particular embodiments, will best be understood by reference to the specication and accompanying drawing, in which Fig. 1 is a circuit diagram of so much of a radio receiver as is necessary to an understanding of my invention, and

Fig. 2 is a series of curves illustrating the operation of my invention.

Referring now more particularly to the drawing, l and 2 represent input terminals to be supplied with signal voltage, which may be derived from the nal I. F. stage of a superheterodyne receiver of the usual type, or from the nal R. F. stage of a tuned radio-frequency receiver.

It will be understood that terminals l and 2 are supplied with only a portion of the voltage output from the receiver, the remainder of the output being supplied to a detector, the output of which may be amplified and operate a loud speaker in the usual manner. A

Connected between terminals I and 2 there may be provided a resistance 30, which may be in the input circuit of amplifier tube 3|. This may be a pentode tube having cathode 3io, control electrode 3| g, screen 3|sc, suppressor 31er, and anode 31a.

Cathode 3l@ may be connected to ground and to one terminal of resistance 30. Control electrode 3 I g may bel connected to the other terminal of resistance 30. Suppressor 3lsr may be connected to cathode 3io and screen 3lsc through resistance 35 to +B and thence to cathode and ground. The output of tube 3! may be passed through a transformer comprising primary 34 and secondary 33, and primary 34 may be connected at one end to anode 3|a and at the other end through resistance 35 to +B.

Condenser 32 may be provided, shunting primary 34, and condenser 33, shunting resistance 35 and the +B source. The secondary of the transformer may be shunted by condensers 31 and 38 in series, the common point of which may be grounded and one terminal of secondary 35 may be connected to one electrode of piezoelectric crystal 39, the other terminal of which may be denser II ,'a's'stted, is'tn' connected through condenser 4I) to the opposite terminal of secondary 36.

The common point of crystal 39 and condenser 40 may be connected to control electrode I4g of control tube I4, which may be a triode having cathode I4c, control electrode I4g, and anode I4a. This tube will preferably be of the thyratron type. Control electrode lgmay be connected through resistance 4i to a variable point onresistance 4I, vvhich'm'ay bein shunt with a suitable biasing battery. Connected between cathode I4c and the terminal of the biasing source, provide switch I4s in the form of ariorni'allyv lclosed pushbutton switch, Which the operatoropens f or a moment when it is desired5toqstart`the tuning r operation. This interrupts the plate circuit of tube I4, deionizing the tube-,"and-starts:the'tuning motor, as will be described. Included in the anode circuit of tube I4 there may be provided relay ,I 5 in seriesvvitlifthe source of platecurrent,

yv suitable'electric'rnotcr mayl 'bei derived rom'any "guia y supply power to armature Ifr,4 of YVcontrol .relay l5 iscarried to The circuit comprising 'ndutaricelll anl'convuit tjbe controlled. givenfbe' in' fthe osciland may, in the exampl grounded and' theother side"- connected to" the Qsc111ator j tube.' sincev suon circuits are' wen 'point through 't etwinding'of yrelay' 22` tov ground in the same 'mannenI Ijhusjyvhen the lelay is in back contact positionQmo'tor I"2 wll'hperate'land Condenser .H will reiste.

" Re'turning'for the "oment'totube slangen/stai DI".acticall matter these ciryz nrange'd as to beconsiderably sharper than this. Preferably theywill havev aband Widthvvhich is only'a small fr'action'of` the bandwidth offthe precedingy circuitsff AsA an e'Xarnple'fbut'not in i limitation., I .have .fcundgiharre'y Saisatory. results are obtainedvvheritli bandwidth in the 'be-used, a4variably-tunedcircuit of great sharpness being substituted.

When the oscillator tuning is such as to bring in asignal of sulcent amplitude to fire tube I4, thesignal-'voltage across the cathode and grid of tube I4 willjrise until on some positive peak A`'thetuoej lires. The strength of signal required to fire tube I4 may be controlled and adjusted by miadjustment ofthe connection to resistance 4 I.

'When this tube fires, the space current sharply increases and the armature or relay I5 is moved toiront contact I5c, interrupting the motor circuit Thereupon thenotor 'st'o'psfthe clutch is disengaged, thebrake applied'to the't'uning condenser, and the formerly'iree Aend of inductance il is' 'c` onnected tof'gro'und This establishes a circuit V consisting of jQmndenser ItV and inductance I'I in parallel With'inductance Iiland condenser 1 I The signiiicance ofthis Will'novv be explained. -Itwvvill be observed that lWhile motor Ai2 is in 1 foperation-and condenser i I is rotating, condenser iB -fan'dvi'nduct'ance I'I haveno effect because the circuit isopen'atcontactlc of relay I5. In my preferred embodiment condenser I may be a continuously variableV condenser operable overSGO" so4 that" contiri uedop'erationof' motor i2 causes c on d` e n ser I to turn repeatedly through its cycle,

j reversal ofhdirection of 'the motor is not necessfn In certain instances in which thetuning is ac- H coniplishedby moving Viron c'o'res'into'and out ofj the inductances this motion may beV accom- --p lished bywa ca rnso arranged that a complete v rotation vof the cam makes a completey tuning cycle, and-in this case valso it is not necessary to Y reverse the motor.

chronism with the' tuning condenser, may be Switch 2 0, operated by cam 2I driven in synprovidedin the V4plate circuit of tube I4 so that dfi-any` overrun of condenser IIv Would be in the during '180 of its 360`rotation d(the return half of the condensercycle; for example, Whenthe capacity is-going from minimum to maiiimum) tube IllV cannot fire. Thus, only one-half of the condensercycle 'for example, when the frequency of the resonant vcircuit increasing) is effectively utilized to stop the tuning. When so arranged direction to increase'the frequency of the'tuned c 'ircuit and thisrnay be compensated for by connecting an additional condenser I6 and inductance I'I' into the circuit after the motor stops.

The value of condenser I6 'and inductance Il willf naturally depend on the specific installation andthe amount of overrun which is encountered,

" Iand it is a relatively simple matter to determine Ybynieasurement and calculation just how much the frequency has increased due to overrun at "any point.

Condenser; IG and inductor I1 may then be 1" chosen Yof the correct value to decrease the frequency by just the desired amount. If tuning condenser EI is a kstraight line capacity condenser,

' 'then inductance VII is frequently not necessary and may be omitted, and satisfactory compensation maybe 'achieved by the use of condenser I6 alone.

'HIjIovtleyerrvvhen condenser Il is of the type customarily"usedfin'which the change of capacity per degree of rotation is not uniform over the range, though the amount of angular overrun is constant, the change in frequency introduced by this overrun will be different at different settings of the condenser, and in such case it is preferable to employ inductance Il in addition to condenser I6.

The connection of condenser I6, and inductance I1, if the latter is used, decreases the resonant frequency of the circuit, and if the correct values are used, the compensation may be made substantially complete over the entire range, and the circuit acts, in effect, as if there were no overrun present.

In the arrangement above described it has been stated that the circuit tuning on which stopping occurs is from minimum to maximum frequency, and the stopping means is rendered ineffective during the cycle from maximum to minimum frequency, but the apparatus may also be arranged to work in the reverse fashion; that is to say, to stop while the frequency is decreasing, and to be ineffective when the frequency is increasing.

If this is done, then the direction of overrun will be to reduce the frequency below what it should be, and instead of connecting condenser I6 and inductance l1 (in case the latter is used) after the tuning has stopped, these elements will preferably be connected in while the tuning is proceeding, and will be disconnected after the tuning has stopped. This may readily be accomplished by providing an additional set of contacts on relay I5.

It will also be understood that by altering the values of condenser I6 and inductance I1 compensation in either direction; i. e., increase in frequency or decrease in frequency, can be obtained with any of the arrangements described. This is of advantage in aifording the designer a considerable latitude in choosing the specific form of circuit and the specific values of the reactances employed to fit to the optimum degree any particular conditions or any particular circuit design encountered.

The amount of compensation required in any particular instance will depend upon a number of factors, among which may be mentioned the speed of the tuning motor, the speed of the tuning instrumentality, the inertia of the moving parts, the nature of the mechanical connection between the motor and the tuning instrumentality, Ithe sensitivity of the control tube, and the frequency range covered.

Three possible conditions may be encountered in the operation of the receiver. First, the signal may be received without noise. Second, noise may be received without signal. Third, both may be received simultaneously. It is desired that the receiver stop scanning the spectrum only on the first and third of these conditions; namely, when a signal is received with or without noise. What is to be -avoided is stoppage when noise only being received.

In the operation of the receiver, suppose the motor to be operating and the receiver to be hunting for an incoming signal which may have the amplitude indicated by a in Fig. 2. The signal-selecting circuits, as previously stated, pass a band which may be 5 kc. in Width, and this means that they will also pass a noise spectrum of the saine width. This may be as indicated in b, wherein the noise amplitude may be considerably greater than the signal amplitude. In

Fig. 2 the noise amplitude b is indicated as apfrom kc. to 0.5 kc. l is reduced correspondingly; that is, from 5 kc. to

proximately three times the signal amplitude. Amplifier tube 3| is operated as a limiter and is adjusted so that it limits at the maximum voltlage developed at the limiter grid by the mini- 'mum or Weakest usable signal in the absence of noise. When this adjustment is properly made,

- it will be found that the receiver will stop scanning the spectrum when any signal of the mini- `may be approximately twice that of value a, but

noise will now be limited to the value d.- No

change in band width has occurred, and both signal and noise may occupy a Spectrum or band 5 kc. wide.

After passing through crystal 39 a significant 'change has occurred. There may be a loss of approximately 50% in amplitude of the signal, as indicated at value e, and at the same time the band width has been reduced to the band width passed by the crystal.

In this instance, the band width is reduced The band width of the noise 0.5 kc., but the amplitude of the noise is reduced in the ratio of the band width of the previous circuits to the band width of the crystal circuit;

- i. e., in the ratio of 5 to 0.5; that is, to T15 of the value of d.. The theoretical explanation of this phenomenon may be somewhat obscure, but there is no question of the fact, as it can be clearly demonstrated.

Since we have now changed the condition shown by curves a and b where the noise exceeded the signal by approximately 3 to 1 to the condition shown in curves e and f Where the signal now exceeds the noise by several times, it now becomes possible to adjust the connection to ref sistance 4l so that the bias voltage `applied to tube I4 lies at some value between the top of curve f and the top of curve e', whereby the noise voltage is insufficient to overcome the bias and thereby fire the tube and stop the tuning, Whereas i the signal voltage, being greater than this value,

' will overcome the bias and fire tube I4.

With a receiver properly adjusted in accordance with my invention and installed in an automobile, I have repeatedly operated the receiver behind trolley cars Where the noise was so great as to mask the signal entirely, and it might be supposed that under such. conditions the tuning had been stopped by the noise, but, by driving far enough away from the. trolleys to reduce the noise, it was always found that the receiver was tuned to an incoming signal which could then be heard, and. this action is so stable and so reliable that once the bias on tube i4 is properly adjusted, the tuning operation may be considered for all practical purposes as entirely immune to false stoppage by noise even under the most extreme conditions. and the receiver will unfailingly operate even Where the noise level is so high lthat the listener `would consider it not Worth .I h-ave contemplated applyingv those principles, =so;as todistinguish my invention from other inventions; ,and 1I have particularly pointed out and distinctly claimed thepa-rt, improvement, or cornbination `which I claim as 'my Ainvention or dis- `l. In Vasignal--seeking receiver of the super- 4heterodyne type having -an intermediate-frecluding in cascade a limiter and a final frequency selector having a much narrower acceptance -frequencyband width than that of said receiver and tuned substantially to the center of the re- -ceiver acceptance frequency band.

2. In a signal-seekmg receiver oi the superheterodyne type having an intermediate-frequency amplifier, `in combination, a circuit to be tuned, Valvariable tuning Vinstrumentality in said circuitfa vmotor forfoperating said tuning instrumentality, a motor-energizing circuit, a control tube responsive to incoming signals, means controlled by said tube for opening said motor cir- -cuitin response to incoming signals, and means for preventing false opening of said motor circuit `by received Ystatic or noise impulses, said last means v.comprising -a circuit interposed rbetween the-output'of the vintermediate frequency amplifier of the receiver and said control tube and including incascade alimiter and a iinel frequency selector having a,much narrower acceptance frequency band width than that of said receiver and tuned substantially -to the center of the receiver acceptance frequency band, whereby normal signalstrength substantially exceeds normal noise level atthe output of said final frequency selector, and means for impressing on said control tube a bias greater than the normal noise strength -but less than normal signal strength.

3. ln a signal-seeking receiver of the superheterodyne type having an intermediate-frequency amplifier, in combination, a circuit to be tuned, a variable tuning instrumentality in said circuit, a motor for operating said tuning instrumentality, a motor-energizing circuit, a control tube responsive `to incoming signals, means controlled by said tube for opening said motor `circuit in response .to incoming signals, and means for preventing false v,opening of said motor circuit by received -static or noise impulses, said last means comprising Va circuit interposed between Ythe output of the intermediate frequency amplifier of the receiver and said control tube and ,including in cascade `a limiter and a final yfrecuency selector having a much narrower acceptance frequency bandwidth than that of said receiver and tunedsubstantially to the center of .the receiver V.acceptance frequency band, whereby normal signal strength substantially exceeds normal noise level .at the `output of said nnal frequency selector, and means for impressing on said control ktube a bias of such value as to prevent response of said tube to normal noise while permitting-.response thereof to normal signals.

v4.1m a signal-.seeking receiver of the superheterodyne type having an vintermediate-frequency famplier, in combination, a circuit to be tuned, a Vvariable tuning instrumentality in said circuit, a motor for operating said tuning instrumentality, a motor-energizing circuit, a control tube responsive to Vincoming signals, means controlled by said tube for opening said motor circuit in response `to incoming signals, and means for preventing false opening of said motor circuit by received Astatic or noise impulses, said last means comprising a circuit interposed between the output of the intermediate frequency amplier of the receiver and said control tube and including in cascade a limiter and a final frequency selector comprising `a piezoelectric crystal having a much narrower acceptance frequency band width than that of said receiver and tuned substantially to the center of the receiver acceptance frequency band.

5. In ka ,signal-seeking Areceiver of the superheterodyne type having an intermediate-frequency amplifier, in combination, a circuit to be tuned, a variable tuning instrumentality in said circuit, motor for operating said tuning instrumentality, ,a motor-energizing circuit, a control tube responsive to incoming signals, means controlled by said tube for opening said motor crcuit in response :to incoming signals, and means for preventing false opening of said motor circuit by received static or noise impulses, said last means comprising v,a Acircuit interposed between the output `of the intermi-:diete frequency amplieier of the receiver and said control tube and including in cascade a limiter and a final frequency selector comprising a piezoelectric crystal having a much narrower acceptance frequency band width than that of said receiver and tuned substantially to thevcenter of the receiver acceptance frequency band, whereby normal signal strength 1 substantially exceeds normal noise level at the output of said final frequency selector, and means for impressing-on said control tube a bias greater than the Vnormal noise strength but less than normal signal strength.

6. In a signal-seeking receiver of the supervheterodyne type `having an intermediate-frequency amplifier, in combination, a circuit to be tuned, a variable .tuning instrumentality in said circuit, a motor foroperating said tuning instrumentality, a motor-energizing circuit, a control tube responsive to incoming signals, means controlled by said tube for opening said motor circuit in response to incoming signals, and means for preventing false opening of said motor circuit by received static or noise impulses, said last means comprising -a circuit interposed between .the output of the intermediate frequency amplifier .of the receiver and said control tube and including in cascade a limiter and a final frequency selector comprising a piezoelectric crystal having a much narrower acceptance frequency band width than that of said receiver and tuned substantially to the center ofthe receiver acceptance frequency band, whereby normal signal strength substantially zexceeds normal noise level at the output of said final frequency selector, and means for impressing onsaid control tube a bias of such value as to prevent response of said tube to normal noise .while permitting response thereoffto normal signals.

7. Inasignal-seeking receiver, in combination, a signal-selecting frequency selective circuit to ne tuned, having a band characteristic of sufficient width to pass voice and music modulate-d signals of usualradio quality, a variable tuning instrumentality in said circuit, a motor for operating said tuning instrumentality, a motorenergizing circuit, a control tube responsive to incoming signals, means controlled by said tube for opening said motor circuit in response to incoming signals, and means interposed between said control tube and said signal-selecting circuit for reducing the amplitude of noise impulses, said last-mentioned means comprising a limiter for limiting noise impulses of the amplitude of desired signals, and a frequency-selective circuit supplied by said limiter, having an acceptance band width substantially narrower than the signal-selecting circuit, and tuned substantially to the center of the receiver acceptance frequency band.

8. In a signal-seeking receiver, in combination, a signal-selecting frequency selective circuit to be tuned, having a band characteristic of sufcient width to pass voice and music modulated signals of usual radio quality, a Variable tuning instrumentality in said circuit, -a motor for operating said tuning instrumentality, a motor-energizing circuit, a control tube responsive to incoming signals, means controlled by said tube for opening said motor circuit in response to incoming signals, and means interposed between said control tube and said signal-selecting circuit for reducing the amplitude of noise impulses, said last-mentioned means comprising a limiter for limiting noise impulses of the amplitude of desired signals, and a frequency-selective circuit including a piezoelectric crystal supplied by said limiter, having an acceptance band Width substantially narrower than the signal-selecting circuit, and tuned substantially to the center of the receiver acceptance frequency band.

9. In a signal-seeking receiver, in combination, a signal-selecting frequency selective circuit to be tuned, having a band characteristic of sumcient width to pass voice and music modulated signals of usual radio quality, a variable tuning instrumentality in said circuit, a motor for operating said tuning instrumentality, a motorenergizing circuit, a control tube responsive to incoming signals, means controlled by said tube for opening said motor circuit in response to incoming signals, and means interposed between said control tube and said signal-selecting circuit for reducing the amplitude of noise impulses, said last-mentioned means comprising a limiter for limiting noise impulses of the amplitude of desired signals, and afrequency-selective circuit including a tuned transformer and a piezoelectric crystal connected to the secondary thereof supplied by said limiter, having an acceptance frequency band Width substantially narrower than the signal-selecting circuit, and tuned substantially to the center of the receiver acceptance frequency band.

VERLIS H. WILEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,056,290 Lowell Oct. 6, 1936 2,231,806 Goldsborough Feb. 11, 1941 2,262,218 Andrews Nov. 11, 1941 2,326,738 Andrews Aug. 17, 1943 FOREIGN PATENTS Number Country Date 425,626 Great Britain Mar. 19, 1935 451,223 Great Britain July 30, 1936" HRWX Certificate of Correction Patent No. 2,491,942 December 2o, 1949 VERLIS H. WILEY It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 66, for quaity read quality; column 4, lines 20 and 31, for 15o read 15j; column 7, line 40, for fine read final send that the said Letters Patent should be read with these corrections therein that me same may conform to the record of the casein the Patent Of'ce.

Signed and sealed this 20th day of June, A. D. 1950.

THUMAS F. MURPHY,

Assistant Uommz'sszoner of Patents.

Certificate of Correction Patent No. 2,491,942 December 20, 1949 VERLIS H. WILEY It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 66, for quaity reed quality; column 4, lines 20 and 31, for 15e read 15j; column 7, line 40, for nel readjnal;

und that the said Letters Patent should be read with these corrections therein that the seme may conform to the record of the casein the Patent Office.

Signed and sealed this 20th day of June, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patente. 

